In his first weeks on the job, Mr. Pruitt drew glowing praise from foes of Mr. Obama’s agenda against global warming, as he moved to roll back its centerpiece, known as the Clean Power Plan, and expressed agreement with those who said the E.P.A. should be eliminated. His actions and statements have galvanized protests from environmentalists and others on the left.

But now a growing chorus of critics on the other end of the political spectrum say Mr. Pruitt has not gone far enough. In particular, they are angry that he has refused to challenge a landmark agency determination known as the endangerment finding, which provides the legal basis for Mr. Obama’s Clean Power Plan and other global warming policies.

These critics say that Mr. Pruitt is hacking only at the branches of current climate policy. They want him to pull it out by the roots.

“The endangerment finding must be redone, or all of this is for naught,” said Steven J. Milloy, who runs a website, JunkScience.com, aimed at debunking the established science of human-caused climate change, and who worked on the Trump administration’s E.P.A. transition team.